i created the file ENABLE_DIAGS and rebooted. So far everthing was fine. i went step by step but the "bug" doesnt work on paperwhite.. so i went back and rebootet and i got back to this bootmenu or whatever.

I tried everthing but now my kindle is freezed! When i press the power button, i see the green led and blink for 3 times and nothing happens :/

That video was a hack for the K4, and the comments posted for it showed various people had problems with it. Many people here have had problems with that method as well on a K4. You tried it on a PW, which is not the same.

Were you actually able to get into the diags menu? Did you rename your 800x600 screensavers folder as shown in the video?

You really show undo your changes. Rename the original 800x600 folder back after deleting the symlink.

Can you see your PW as a USB device from your host PC?

Some of your described behavior seems inconsistent with how I understand the behavior of a PW. What firmware version do you have on it?

Diags will drain your battery. Plug it into a wall charger. To exit diags you need to create a missing xml file and folder. You can do that by selecting the first diag in the main diags menu. Then select "disable diags" from the exit menu. That will delete ENABLE_DIAGS and reboot to main mode.

When i tried it and then i disable diags i get the error: Could not mound/access customer partition

No!

Look at the screenshot you posted above. Is "L) Device info from xml file" the first selection on the main diags menu? No, it is not. Why did you select it?

What is the first selection on the menu, as shown in your screenshot, that I told you to choose? According to your screenshot photo, it is "S) Device Setting". Perhaps you should try doing what I told you. Just select it, then exit. Do not make any changes while in there. Okay? After that, the missing xml file should have been created.

You are lucky that the thing you selected did NOT corrupt your device info (idme vars)...

The latest menu you are in wants input from the serial port. I have told you NOT to do anything in that menu. Just go into it and then exit it. If you keep doing things I did not say to do, or things I said NOT to do, you will get yourself into a worse situation.